1. Field of the Invention
The present invention relates to a sheet post-processing apparatus for applying a specified post-processing to sheets fed from an image forming apparatus such as a copier, a facsimile machine or a printer.
2. Description of the Related Art
There has been known a sheet post-processing apparatus for applying a specified post-processing to sheets conveyed from an image forming apparatus. This sheet post-processing apparatus successively receives and aligns sheets fed from the image forming apparatus installed at an upstream side in a main storing section, and discharges the sheets after applying a post-processing such as stapling with a unit set of sheets (one bundle) stored.
Normally, in the sheet post-processing apparatus, the sheets of one bundle can be received one by one in accordance with sheet feeding intervals from the image forming apparatus. However, since longer time is taken to staple a specified number of sheets forming one unit set with these sheets stored in the storing section, it is not possible to deal with the sheets successively fed from the image forming apparatus. It has been a general practice to temporarily suspend the operation of the image forming apparatus in order to solve this problem. However, this leads to the temporary suspension of an image formation processing, which causes a problem of reducing the processing efficiency of the image formation processing including the post-processing.
A sheet post-processing apparatus disclosed in Japanese Unexamined Patent Publication No. 2004-246056 temporarily stores the first one of a plurality of sheets of one bundle fed from an image forming apparatus on the circumferential surface of a temporarily storing drum as an auxiliary storing section separately provided, and staples the bundle of sheets stored in a storing section during the temporary storage of the first sheet. The sheet temporarily save on the temporarily storing drum is fed to the storing section emptied upon completing the stabling to the previous bundle of sheets while accompanying the next sheet conveyed from the image forming apparatus. By employing such a measure, it is not necessary to temporarily suspend the image formation processing and, accordingly, the processing efficiency of the image forming apparatus can be improved.
Japanese Unexamined Patent Publication No. 2004-246056 also discloses another mode in which temporary storage on the temporarily storing drum is applied not only to the first sheet of the bundle of sheets, but also to all the sheets and, for example, the sheets are alternately temporarily saved on the temporarily storing drum to feed the one sheet temporarily stored and the next sheet together to the storing section. By feeding the two sheets to the storing section together, a time required to align the sheets in the storing section is partly compensated for by the temporarily storage of the sheets, wherefore more sheets can be processed per unit time to speed up the image formation processing.
In the sheet processing apparatus disclosed in the above publication, if the sheets are alternately saved on the temporarily storing drum by applying the temporary storage not only to the first sheet of one bundle, but also to all the sheets, the last sheet cannot be temporarily saved on the temporarily storing drum after the sheets are fed in pairs to the storing section in the case where the number of the sheets in one bundle is an odd number (i.e., the last sheet is fed to the storing section while accompanying the first sheet of the next bundle if being temporarily stored), with the result that a time required for the post processing in the main storing section cannot be ensured.
In order to solve such a problem, in the apparatus disclosed in the above publication, the first sheet of the next bundle being conveyed is temporarily suspended and the last sheet of the previous bundle is fed to the storing section during the temporary suspension of the conveyance to apply a specified post-processing to this bundle of sheets.
However, if the conveyance of the first sheet of the next bundle is temporarily stopped, it leads to the necessity to also temporarily suspend the image formation processing. This causes a problem of reducing the processing efficiency of the entire image formation processing.